Korean J Sports Med.  2020 Dec;38(4):199-207. 10.5763/kjsm.2020.38.4.199.

Changes in Shoulder Muscle Activities Depending on Static and Dynamic Body Positions during Shoulder External Rotation Exercises Using Kinetic Chain Concept

Affiliations
  • 1Department of Orthopaedic Surgery, Konkuk University Hospital, Konkuk University School of Medicine, Seoul, Korea

Abstract

Purpose
We aimed to evaluate shoulder muscle activities during shoulder external rotation exercises using an elastic band with the arm at the side or at 90° of abduction in static and dynamic body positions.
Methods
In 2017, a total of 19 right-handed male subjects were included in this study. Surface electromyography signals were recorded from the anterior deltoid, middle deltoid, upper trapezius, lower trapezius, serratus anterior, and infraspinatus muscles. The subjects underwent maximal voluntary isometric contraction testing of each muscle in the W position or 90/90 position. Subjects performed the exercise in the sitting, static squat, static rotational squat, dynamic squat to standing (DSS), and dynamic squat to standing and trunk rotation (DSSR) positions.
Results
The main finding of this study was that shoulder external rotation exercises in the DSSR position were effective in reducing shoulder muscle activities except in the serratus anterior compared with static rotational squat position.
Conclusion
DSSR enabled effective control of scapular motion with less shoulder muscle activation. Therefore, the kinetic chain exercises incorporated with lower extremity, hip, or trunk would be beneficial for shoulder muscle exercises, which is required for patients with weak periscapular muscles, in whom the lower trapezius activities were found to be frequently decreased.

Keyword

Electromyography; Muscles; Shoulder

Figure

  • Fig. 1 Position of shoulder external rotation exercise. (A) 90/ 90 position. (B) W position.

  • Fig. 2 Shoulder external rotation exercises using an elastic band with 90° of shoulder abduction and ER (90/90 position) in static (A−C, F−H) and dynamic body positions (D, E, I, J). (A, F) Sitting position. (B, G) Static squat position. (C, H) Static rotational squat position. (D, I) Dynamic squat to standing position. (E, J) Dynamic squat to standing and trunk rotation position.

  • Fig. 3 Muscle activities of anterior deltoid (AD), middle deltoid (MD), upper trapezius (UT), lower trapezius (LT), serratus anterior (SA), and infraspinatus (IS). EMG: electromyography, MVIC: maximum voluntary isometric contraction, SS: static squat, SRS: static rotational squat, DSS: dynamic squat to standing, DSSR: dynamic squat to standing and trunk rotation.


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